Display UV-Map node input in panel
UILayout.prop_search

Test code, draw method, looks for all uv map nodes on the active object's active material nodes, adds a prop search to each listing all the uvmaps on the objects mesh.  The search data is the mesh, the search property is "uv_layers" and the name of each layer is displayed in the prop search menu.

def draw(self, context):
    layout = self.layout
    col = layout.column()

    obj = context.object
    me = obj.data
    mat = obj.active_material
    nodes = [n for n in mat.node_tree.nodes if n.type == 'UVMAP']
    for n in nodes:
        col.prop_search(n, "uv_map", me, "uv_layers")